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Fewer and fewer stars in the sky. Light pollution is progressing at a lightning pace

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The latest study by an international group of scientists has indicated that the night sky becomes 9.6 percent brighter on average every year. The authors warn that this phenomenon, known as light pollution, may have an adverse effect not only on astronomical observations.

Artificial lighting at night has become an integral part of human life. However, the luminous glow that extends over cities and roads is an obstacle to astronomical observations and can also contribute to many negative environmental and health effects. According to a study published in the journal Science, light pollution is progressing at a much faster pace than we thought.

150 stars lost

Scientists from the German Institute for Geosciences (GFZ) and the research institute NOIRLab in Arizona based their study on data provided by amateur astronomers between 2011 and 2022. Observers from around the world tried to observe the faintest stars in the night sky in their area – the stronger the background glow, the fewer objects could be seen. On this basis, the authors of the study calculated changes in the brightness of the sky in different places on Earth.

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The analysis indicated that the rate at which stars become invisible to city dwellers is dramatically fast. The global average annual increase in the brightness of the night sky was 9.6 percent. The rate of increase varied by region: in Europe, the sky was getting 6.5 percent brighter year on year, while in North America the rate was 10.4 percent.

– Let’s assume that the increase in brightness proceeds at an average global rate. If a child is born in a place where 250 stars are visible, then when he reaches the age of majority, he will see only 100 stars in the same point – explains Christopher Kyba from GFZ, the lead author of the study.

Satellites can’t see everything

The results were a big surprise to scientists, mainly because they did not fully match the data obtained in satellite measurements. They indicated a much slower increase in the brightness of artificial lighting, and in places even a decrease. Researchers speculate that this is largely due to the way satellite sensors work.

“Satellites are most sensitive to light that is directed upwards, but this light emitted horizontally makes up the majority of the glow,” explains Kyba. – Large, bright advertisements and facade ornaments can have a large impact on the brightness of the sky in the city, without making a big difference in satellite images.

Another important factor is the widespread shift from orange sodium lamps to white LEDs, which emit much more blue light. Human eyes are very sensitive to blue light at night, but satellite sensors have trouble detecting it. In addition, blue light is more easily dispersed in the atmosphere, enhancing the glow effect.

Beautiful but dangerous

Scientists point out that light pollution affects not only stargazing and astronomical research, but also the natural environment. Commenting on the study, Fabio Falchi and Salvador Bara of the University of Santiago de Compostela add that many of the physiological processes of living beings are determined by circadian and seasonal cycles, so light and dark directly affect them.

Exposure to artificial light at night also reduces melatonin production in animals, including humans. Melatonin is the primary hormone that controls the animals’ internal circadian clock and thus the animals’ physiology. The lack of this hormone can have numerous negative health consequences.

– When looking at pictures and videos taken by the International Space Station, people are generally struck by the “beauty” of city lights, as if they were lights on a Christmas tree. It’s like admiring a gasoline rainbow on the water without knowing that we are dealing with pollution, they add.

Main photo source: Shutterstock

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